Semiconductor integrated circuit device

ABSTRACT

A semiconductor integrated circuit device for minimizing clock skew over clock wiring shortened for reduced wiring delays. A plurality of stages of clock drivers are provided on clock wiring paths ranging from a clock generator to flip-flops. Clock lines connecting upper stage clock drivers are equalized in length in the form of a tree structure, and clock lines connecting lower stage clock drivers are made as short as possible.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a semiconductor integratedcircuit device and, more particularly, to a semiconductor integratedcircuit device having clock wiring with reduced clock skew.

[0002] Some semiconductor integrated circuit devices, such as VLSIs,include a synchronous circuit having flip-flops driven by a common clocksignal. To make such a synchronous circuit operate more rapidly, thesesemiconductor integrated circuit devices require that clock skew (i.e.,differences in clock supply timing between flip-flops) be minimized forremoval of signal-to-signal timing differences.

[0003] Various layout design techniques for reducing such clock skewhave been proposed. One such technique involves installingtree-structure paths between a clock signal generator and a plurality offlip-flops, wherein the length of the path between the generator andeach flip-flop is suitably adjusted. Another technique, which isdisclosed in Japanese Published Unexamined Patent Application No. Hei9-307069, requires inserting clock buffers where appropriate whentree-structure wiring has been established, whereby the tree structureis readjusted so that the difference between a maximum and a minimum ofdelays on the readjusted wiring attains a predetermined value. Wherethere still remains clock skew despite the provision of tree structurewiring, another technique disclosed in Japanese Published UnexaminedPatent Application No Hei 8-274260 seeks to minimize the skew byreplacing appropriate drivers with small-capacity drivers so that thepaths with maximum skew become equal in skew level to other tree branchpaths between second stage clock drivers and block circuits.

[0004] The conventional techniques outlined above have failed toconsider optimum arrangements of skew reduction for VLSIs. Thesetechniques presuppose that on tree-structure paths between a clockgenerator and each flip-flop, each node is afforded wiring of an equallength. If equal-length wiring is provided ranging from a clockgenerator through a plurality of stages of drivers to flip-flops,alternative lines necessitated by the equal-length lines at all stagesprolong the overall clock wiring. The resulting disadvantages includemore delays of clock signals and higher power dissipation.

[0005] Furthermore, the conventional techniques above have disregardedan optimum clock layout for each of the functional portions or for eachof a plurality of clock phases in connection with LSIs. A VLSI comprisesrandom logic circuits and data paths reflecting various functions of thedevice, as well as numerous I/O pads. The conventional techniques haveso far shied away from providing any optimum clock layout for thediverse internal arrangements of the LSI.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the present invention to provide asemiconductor integrated circuit device having a clock skew-loweringlayout that ensures reduced wiring delays, enhanced packaging densityand low clock power dissipation.

[0007] It is another object of the present invention to provide asemiconductor integrated circuit device having an optimum clock layoutcorresponding to each of the functional portions constituting an LSI.

[0008] These and other objects, features and advantages of the inventionwill become more apparent upon a reading of the following descriptionand appended drawings.

[0009] Major features and benefits of the invention are outlined below.In carrying out the invention, and according to one aspect thereof,there is provided a semiconductor integrated circuit device comprising aplurality of stages of clock drivers furnished on clock wiring pathsranging from a clock generator to flip-flops. Clock lines connectingupper stage clock drivers have an equal length each in the form of atree structure, and clock lines connecting lower stage clock drivershave the shortest possible lengths.

[0010] The lower the stage, the greater the number of clock driversfurnished. In that structure, clock lines connecting lower stage clockdrivers are made to have not equal lengths but the shortest possiblelengths. The arrangement shortens the overall clock wiring, reduceswiring delays, enhances packaging density, and lowers clock powerdissipation. Since the lower stage clock drivers are connected by linesthat are shorter than those connecting the upper stage clock drivers,the lower stage clock drivers may have the shortest possible wiringentailing negligible clock skew. Because the upper stage clock driversare connected by extended wiring, the lines constituting such wiring aremade to be equal in length in order to minimize clock skew.

[0011] A semiconductor integrated circuit device according to anotheraspect of the invention also comprises a plurality of stages of clockdrivers. Of these drivers, intermediate stage clock drivers are providedwith clock logic circuits for controlling clock signal supply.

[0012] The clock logic circuits control the supply of clock signals toindividual function blocks corresponding to the intermediate clockdrivers in question. The setup implements a clock signal supply schemesuitable for a VLSI while minimizing clock skew. Preferably,next-to-last stage clock drivers may have clock logic circuits forsupply of clock signals to the flip-flops of random logic circuits andinput/output pads, and both last stage and next-to-last stage clockdrivers may have clock logic circuits for the supply of clock signals tothe flip-flops of data paths.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic circuit diagram of clock logic circuitsapplicable to a semiconductor integrated circuit device embodying theinvention;

[0014]FIG. 2 is a top view of a clock layout on a chip carrying thesemiconductor integrated circuit device embodying the invention:

[0015]FIG. 3 is a detailed plan view of the layout of a region 204 inFIG. 2;

[0016]FIG. 4 is a more detailed plan view of the vicinity of a region301 in FIG. 3;

[0017]FIG. 5 is a detailed plan view of the layout of a region 206 inFIG. 2;

[0018]FIG. 6 is a more detailed plan view of the layout of a region 504in FIG. 5;

[0019]FIG. 7 is a set of schematic views depicting relations betweenclock drivers at different stages on the one hand and logic blocks onthe other hand in the inventive semiconductor integrated circuit device;

[0020]FIG. 8 is a set of layout diagrams illustrating relations betweenthe regions handled by the second stage clock drivers shown in FIG. 7 onthe one hand and logic blocks on the other hand;

[0021]FIG. 9 is a detailed plan view of clock drivers laid out in datapaths;

[0022]FIG. 10 is a detailed plan view of clock drivers laid out in aninput/output pad;

[0023]FIG. 11 is a conceptual diagram showing how different stages ofthe inventive semiconductor integrated circuit device are typicallywired;

[0024]FIG. 12 is a set of explanatory diagrams indicating howdifferences between clock delays are reduced over different paths by useof clock wiring 1102;

[0025]FIG. 13 is a schematic view depicting typical clock wiring rangingfrom second stage clock drivers to third stage clock drivers; and

[0026]FIG. 14 is a partially enlarged view of the clock wiring from thesecond stage clock drivers to the third stage clock drivers in FIG. 13.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027]FIG. 1 is a schematic diagram showing clock logic circuitsapplicable to a semiconductor integrated circuit device embodying theinvention. This embodiment comprises four stages of clock driversthrough which a clock signal generator 101 supplies clock signals to allflip-flops 106 inside the chip. The flip-flops are located in randomlogic circuits, data paths, and input/output pads.

[0028] The clock drivers at each stage play the roles described below.Clock drivers 102, situated at the first stage as viewed from the clocksignal generator, are called root clock drivers. These driversdistribute throughout the entire chip the clock signals output by theclock signal generator.

[0029] Second stage clock drivers 103 distribute clock signals to thirdstage clock drivers 104. The drivers 104 are located in regions eachmade up of a number of logic blocks in the chip.

[0030] The third stage clock drivers 104 and fourth stage clock drivers105 serve to distribute clock signals to all flip-flops in the logicblocks. If the third stage clock drivers 104 are constituted logicallyto control the supply of clock signals, it is possible to control clocksignal supplies on a block-by-block basis.

[0031] Each third stage clock driver 104 supplies clock signals to agroup of fourth stage clock drivers 105 distributed in each of the logicblocks. The fourth stage clock drivers 105 supply clock signals directlyto the flip-flops 106. Each driver 105 feeds clock signals to a group offlip-flops 106 distributed in the logic blocks of random logic circuits.Each data path 209 supplies clock signals to a column of flip-flops 113via a clock terminal 114. Each I/P pad portion 202 feeds clock signalsto flip-flops 119 within a predetermined distance by means of clockterminals 118.

[0032] The third stage clock drivers 104 are provided as AND circuitseach having a control signal input terminal 107. All third stage clockdrivers 104 inside each of the logic blocks are connected to a signalline 108 that controls the supply of clock signals within the block inquestion. With the third stage clock drivers 104 provided as ANDcircuits, there is no need to provide each fourth stage clock driver 105as an AND circuit. This minimizes the number of clock drivers that needto be replaced by AND circuits. A reduction in the number of clockdrivers replaced by AND circuits directly translates into a reduction inthe lengths of the control signal lines.

[0033] The concept sketched in FIG. 1 is not limited to a single-phaseclock scheme; it is obviously applicable to multi-phase clockarrangements as well. The semiconductor integrated circuit device ofthis embodiment includes three lines 302 coming from the clock signalgenerator and implementing a three-phase clock scheme, as shown in FIG.3. The three-phase clock scheme generates three kinds of clock signal: afirst clock signal, the fastest clock signal fed to a CPU and an FPU inthe semiconductor integrated circuit device; a second clock signalsupplied to bus access controllers such as a DMAC (direct memory accesscontroller) and I/O pads; and a third clock signal fed to peripheralcontrollers. In FIG. 3, three root clock driver layout regions 301 arefurnished to match the three clock signals of the three-phase clockscheme. For purpose of explanation, FIG. 1 indicates in unified fashionthe three kinds of clock signal: one clock signal fed to the flip-flops(106, 109) of the random logic circuits; another clock signal suppliedto the flip-flops (113) of the data paths; and another clock signal fedto the flip-flops (119) of the I/O pads. Of the three-phase clocksignals, the first clock signal is sent to the random logic circuits anddata paths, the second clock signal is given to the random logiccircuits and I/O pads, and the third clock signal is delivered to therandom logic circuits.

[0034] Some flip-flops admit control signals, while others do not. Therandom logic circuits and I/O pads contain both types of flip-flops. Thedata paths 209 have no flip-flops admitting control signals. Instead,all flip-flops arranged in each single column are controlledcollectively by a clock driver 112 that serves as an AND circuit havinga control signal input terminal 115. Where control signals are input tothe last stage clock drivers 112 on the data paths, the flip-flopsinside the data paths have no need for control terminals. This structureenhances the packaging density of the embodiment.

[0035] A low clock skew state is brought about by unifying differencesin arrival time between clock signals sent from the clock signalgenerator 101 to all flip-flops (called clock delays hereunder). Tounify the clock delays requires adjusting both the driving force ofclock drivers and the load capacities associated with the clock drivers.The load capacity of a clock driver is determined by the total sum ofthe capacity of a line connected to the driver in question and thecapacity of the input terminal of a fan-out destination cell. In thelogic setup of this embodiment, the driving forces of the clock driversat each stage and the load capacities associated therewith are adjustedso as to unify the clock delays involved, thereby harmonizing all clockdelays. The clock drivers 102 and 103 use cells of the same typethroughout all paths, each driver having an identical fan-out count andan equal wiring length. The clock drivers 104 and 105 have differentfan-out counts at each stage but share the same total capacity includingwiring capacity, with the exception of the clock drivers 112 on the datapaths. For example, if fan-out destination clock drivers are far away sothat the wiring involved is necessarily long, the fan-out count tends tobe small. Conversely, if clock drivers are nearby, the fan-out count islikely to be large. Each clock driver 112 on a data path has up to 32flip-flops 113 within the path. Thus the clock drivers 112 have greatercapacities than the clock drivers of the random logic circuits. For thatreason, clock drivers with high driving forces are used at the laststage to harmonize the clock delays with those of the random logiccircuits and I/O pads. Thanks to the above-described four-stage clocklogic arrangement over all paths, clock delays may be adjusted at eachstage.

[0036] Where multi-phase clock signals are used, similar logicalstructures are instituted. Because all phases are matched with likelogical structures, there occurs little key skew between the multi-phaseclock signals.

[0037]FIG. 2 shows a clock layout on a chip 201 carrying thesemiconductor integrated circuit device embodying the invention. In FIG.2, the clock signal generator 101 is located in a corner of the chip 201and adjacent to an I/O pad portion 202.

[0038] All clock drivers are furnished in a cell layout region 203. Theroot clock drivers 102 are gathered together in a region 204 near thechip center. The clock signal generator 101, which is vulnerable toadverse effects from other circuits, is located peripherally in thechip. The root clock driver 102 located centrally in the chip extendsclock wiring to the downstream root clock driver. This setup ensuresstable supply of clock signals and makes it easier to minimize clockskew.

[0039] Some second stage clock drivers 103 are allocated to a region 206that comprises a number of logic blocks. Second stage clock drivers 103assigned to the data path 209 are located in a clock driver layoutregion 207 on the clock terminal side of the data paths. Likewise,second stage clock drivers 103 destined for the I/O pad portions 202 arefurnished in a clock driver layout region 208 on the clock terminal sideof each pad.

[0040]FIG. 3 depicts in detail the layout of the region 204 in FIG. 2.As mentioned earlier, what FIG. 3 portrays is a three-phase clocklayout. The root clock drivers 102 are gathered together in regions 301that are each adjacent to a power supply line 303. Reference numeral 302denotes signal lines coming from the clock signal generator.

[0041] In this multi-phase setup, the root clock drivers 102 for eachclock phase flank a vertical power supply line 303 and a horizontalpower supply line 304. The clock lines 302 leading to the clock driverlayout regions 301 for all clock phases run in parallel up to a point305 where the lines are branched, the point 305 being at an equaldistance from all clock driver layout regions. Because the clock driverlayout regions are not concentrated on a single power supply line, thesupply of power is stabilized. The wiring arrangement above makes theline lengths substantially equal for all phases between the clock signalgenerator 101 and each of the root clock drivers 102.

[0042]FIG. 4 provides a more detailed view of the vicinity of one region301 in FIG. 3. As illustrated, the root clock drivers 102 in the region301 are arranged adjacent to one another in the vertical direction.There is no other cell interposed between each root clock driver 102 andthe power supply line 303. With the root clock drivers 102 gathered nearthe chip center, the lines ranging from the clock signal generator toall root clock drivers 102 are made equal in length. Because the maximumdistance between the root clock drivers 102 and the second stage clockdrivers 103 is reduced, clock delays are lowered correspondingly. Wherethe regions 301 are located adjacent to the power supply lines, it ispossible to supply power in a stable manner to the regions where aplurality of root clock drivers 102 are gathered together.

[0043]FIG. 5 gives a detailed view of the layout of the region 206 inFIG. 2. The second stage clock driver 103 in the region 206 is locatednear the center of gravity of a plurality of third stage clock drivers104 distributed within the same region. Lines making up a network 501ranging from the second stage clock driver 103 to the third stage clockdrivers 104 are equalized in length.

[0044] Each third stage clock driver 104 is allocated to a region 502wherein fourth stage clock drivers 105 are gathered adjacent to oneanother. Lines constituting a network 503 ranging from the third stageclock driver 104 to the fourth stage clock drivers 105 are equalized inlength.

[0045]FIG. 6 gives a more detailed view of the layout of a region 504 inFIG. 5. As illustrated, each fourth stage clock driver 105 is allocatedto the region 504 wherein flip-flops 106 are gathered adjacent to oneanother. Lines making up a network 601 ranging from the fourth stageclock driver 105 to the flip-flops 106 are equalized in length.

[0046]FIG. 7 provides a set of schematic views depicting relationsbetween clock drivers at different stages on the one hand and logicblocks on the other hand in the inventive semiconductor integratedcircuit device. Each of the regions 206 comprises either a plurality oflogic blocks or part of a logic block. Logic blocks wherein the numberof third stage clock drivers 104 is smaller than a reference fan-outcount of the second stage clock driver 103 are gathered together; logicblocks wherein the number of third stage clock drivers 104 is largerthan the reference fan-out count are each divided into smaller regions.

[0047] Illustratively, logic blocks 702, 703 and 704 wherein the numberof third stage clock drivers 104 is smaller than the reference fan-outcount are gathered together in a region 705 handled by a second stageclock driver 701. On the other hand, a logic block 708 in which thenumber of third stage clock drivers 104 is larger than the referencefan-out count is divided into regions 709 and 710. The region 709 ishandled by a second stage clock driver 706, and the region 710 is dealtwith by a second stage clock driver 707. Reference numeral 711 in thissetup denotes a root clock driver.

[0048] However, it is not desirable to establish a logical structuresuch as one of a region 718 that is divided into regions 714 and 717,the region 714 being handled by a second stage clock driver 713connected to a root clock driver 712, the region 717 being dealt with bya second stage clock driver 716 coupled to another root clock driver715. This type of logical structure will give rise to a possibility thata single logic block can be subject to adverse effects of the clock skewover relatively long wiring between the clock signal generator and theroot clock drivers.

[0049] Where the number of clock drivers is smaller than the referencefan-out count inside a region 720 handled by a second stage clock driver719, dummy cells 721 are added to the region to compensate for theshortage of clock drivers. A dummy cell is a cell of which the inputcapacity is the same as that of a clock driver connected to the samenetwork and which does not use output signals of the network.

[0050] As described, the fan-out count of the second clock driver 103may be taken as the reference value with respect to which adjustmentsare made as needed. This makes it possible to harmonize on all paths theclock delays stemming from the second clock drivers 103.

[0051]FIG. 8 provides a set of layout diagrams illustrating relationsbetween the regions handled by the second stage clock drivers shown inFIG. 7 on the one hand and logic blocks on the other hand.Illustratively, if the reference fan-out count of a second stage clockdriver 809 is 4, then a logic block 803, in which the number of thirdstage clock drivers 802 is greater than the reference fan-out count, isdivided into regions 810 and 811. Third stage clock drivers in each ofthe regions 810 and 811 are assigned a second stage clock driver 809.How to divide a logic block is determined by the arrangement of thirdstage clock drivers 802 furnished therein. If the clock driver count ina divided region is smaller than the reference fan-out count, thenpreviously furnished dummy cells 814 are used to take the place of thirdstage clock drivers 802 to compensate for the shortage of clock drivers.Meanwhile, each of logic blocks 804, 805, 806, 807 and 808 has a smallernumber of third stage clock drivers 802 than the reference fan-outcount. In such cases, adjacent logic blocks are gathered together toform a single region to which a second stage clock driver 809 isallocated.

[0052] In FIG. 8, the logic blocks 804, 805 and 806 are combined into aregion 812, and the logic blocks 807 and 808 into a region 813. Wherethe number of third stage clock drivers 802 is smaller than thereference fan-out count inside a combined region, previously furnisheddummy cells 814 are utilized to compensate for the shortage with respectto the fan-out count of the second stage clock driver 809.

[0053]FIG. 9 is a detailed view of clock drivers laid out in data paths209 shown in FIG. 2. A clock terminal 902 is allocated to each column offlip-flops 901 in the data paths 209. The clock terminals 902 arearranged so as to line up on one side of the data paths 209.

[0054] A clock driver layout region 207 is provided on a cell layoutregion 907 on the side of the clock terminals 902 for the data paths.Inside the clock driver layout region 207 are third stage clock drivers905 and fourth stage clock drivers 906.

[0055] The clock driver layout region 207 is also arranged to beadjacent to a power supply line 904. If clock drivers of the data pathsare located on the cell layout region, it is possible to gather clockdrivers together where the clock terminals are concentrated. This helpsprevent a surge in clock delays. Providing the clock driver layoutregion forestalls increases of distances up to the clock drivers.Although the clock drivers of the data paths are considerablyconcentrated in terms of layout because of their numerous clockterminals, locating the clock driver layout region adjacent to the powersupply line ensures stable supply of power.

[0056] Although not shown, there exist a large number of third stageclock drivers 905 of the data paths. In this setup, the wiring betweenthe second stage clock drivers 103 and the third stage clock drivers 905of the data paths is furnished as follows: a plurality of third stageclock drivers are grouped together, and the wiring within that group ismade as short as possible. Lines between the second stage clock drivers103 and the respective groups of third stage clock drivers are equalizedin length.

[0057]FIG. 10 provides a detailed view of clock drivers laid out in theI/O pad portion 202 shown in FIG. 2. A clock terminal 1002 is allocatedto each flip-flop 1001 inside the I/O pad portion 202. The clockterminals 1002 are arranged so as to line up on one side of the I/O padportion 202. A clock driver layout region 208 is furnished on a celllayout region 1006 on the side of the clock terminals 1002 in the I/Opad portion 202. Inside the clock driver layout region 208 are third andfourth stage clock drivers 1004 and 1003 arranged in a row, each thirdstage clock driver being flanked by a plurality of fourth stage clockdrivers. A reference wiring length is set for the fourth stage clockdrivers 1003, and as many clock terminals 1002 as a reference fan-outcount are allocated within the reference wiring length. This arrangementis adopted here because the number of clock terminals are small despitethe long distance occupied by them in the I/O pad portion 202.

[0058] If there are fewer clock terminals within the reference wiringlength 1007 than the reference fan-out count, then dummy cells 1005 areadded to compensate for the shortage.

[0059] When the layout regions are furnished as described, any increasesin the distances up to the clock drivers are substantially prevented.The use of numerous dummy cells makes it possible to harmonize clockdelays despite the presence of sparsely arranged clock terminals.

[0060] The dummy cells 1005 should preferably be arranged in the samerow as that of a plurality of clock drivers as illustrated in FIG. 10.That is because the arrangement facilitates adjustment of the wiringlengths while minimizing increases in occupied areas.

[0061] In FIG. 10, one fourth stage clock driver 1003 is furnishedcorresponding to four clock terminals. However, the one-to-fourcorrespondence is not limitative of the invention. For example, supposethat each fourth stage clock driver 1003 is assigned 12 terminals andthat only one flip-flop 1001 is connected to a fourth stage clock driver1003. In that case, 11 dummy cells 1005 may be connected to the fourthstage clock driver 1003 in question.

[0062] In the I/O pad portion 202, each flip-flop 1001 is associatedwith an input/output circuit 1008 and an I/O pad 1009 which are arrangedin the direction of a chip edge. In the inventive semiconductorintegrated circuit device, the logic circuits inside of the I/O padportions 202 use signals with an amplitude of 1.8 V, and are interfacedto signals with an amplitude of 3.3 V from outside the chip. Theinterface capability is implemented by use of a level shifter circuitarrangement. More specifically, each I/O circuit 1008 includes athree-state logic circuit, a level shifter circuit and an I/O buffercircuit arranged in that order starting from the flip-flop side. Thesecircuits are connected to an I/O pad 1009.

[0063]FIG. 11 gives a conceptual view illustrating how different stagesof the inventive semiconductor integrated circuit device are typicallywired. Lines 1102 and 1103 are equalized in length and constitute abinary tree structure. Lines 1104 and 1105 are made as short aspossible. That is, the lines at a higher stage where fan-out destinationcells are distributed extensively are equalized in length; wiring at alower stage where fan-out destination cells are narrowly distributed ismade the shortest possible wiring Length differences (i.e., between amaximum and a minimum length) between clock lines equalized in lengthare smaller than length differences between clock lines that are made asshort as possible.

[0064] Wiring 1101 is provided at the highest stage However, since thiswiring involves root clock drivers 102 gathered together as shown inFIG. 4, it is prepared as the shortest possible wiring.

[0065] The lines 1102 and 1103, with their fan-out destination cellsdistributed extensively, are equalized in length on all paths. Thisarrangement helps harmonize clock delays over the paths.

[0066] The above adjustments are made possible because the number ofclock drivers at the upper stages is limited. The lower the stage, thegreater the number of clock drivers installed. Thus the lines are madeas short as possible at lower stages in order to reduce the overallwiring length, boost packaging density and minimize line-induced delays.Because the wiring is shorter at lower stages, clock skew stemming fromthe line-induced delays is negligible there.

[0067] At higher stages where extended wiring promotes vulnerability todelays, the lines involved are equalized in length so as to reduce theclock skew caused by the line-induced delays. When all lines areequalized in length on all paths, differences in load capacity betweenclock drivers are eliminated.

[0068]FIG. 12 offers a set of explanatory views indicating howdifferences between clock delays are reduced over different paths by useof the clock wiring 1102. It may happen that differences in clock delay1202 exist between second stage clock drivers 103 and flip-flops 106.Such differences, if they occur, are reduced by modifying theconfiguration of the lines 1102 which are basically equalized in lengthand which constitute a binary tree structure. Specifically, clock delays1201 are adjusted between the root clock drivers 102 and the secondstage clock drivers 103. For example, if there are clock delaydifferences between each of two second stage clock drivers 103 connectedto a line 1102 on the one hand and the corresponding flip-flops 106 onthe other hand, the lengths of lines 1205 and 1206 between a junction1207 and the second stage clock drivers 103 are adjusted at the point1207 in such a manner that the clock delay differences are removed. Anyclock delay differences that may occur between another root clock driver102 and the second stage clock drivers 103 are eliminated by adjustingthe length of a line 1204 between the clock driver 102 and the junction1207. Such adjustments, which are relatively simply in procedure and arerequired at only a small number of locations, may be carried outmanually.

[0069] Where clock drivers of high driving forces are used, lines widerthan usual need to be employed to counter migration. Because theincidence of migration is proportional to the strength of current, thewiring need only be composed of wide lines up to first junctions beyondwhich the current strength is reduced by half. Along clock wiring 1301between a second stage clock driver 103 and third stage clock drivers104 in FIG. 13, a portion 1302 is made of a wide line (having twice thewidth of ordinary wiring) as shown in FIG. 14. The rest of the wiringhas the ordinary width such as that of a portion 1401. An outputterminal 1402 of each second stage clock driver 103 is shaped as arectangle at least as broad as the wide line so that the latter may beconnected properly to the terminal 1402. Where there are a limitednumber of locations requiring wide-line wiring, packaging density isimproved.

[0070] Wide-line wiring is not limited to the clock wiring between thesecond stage clock drivers 103 and the third stage clock drivers 104. Itis also possible to install wide lines up to the first junctions alongthe clock wiring between the root clock drivers 102 on the one hand andthe second clock drivers 103 on the other hand.

[0071] As described, a semiconductor integrated circuit device havingthe inventive clock layout is subject to significantly reduced wiringdelays, has increased packaging density, and provides a clockskew-lowering layout involving decreased clock power dissipation. Thedevice also has an optimally arranged clock layout for each functionalportion of the LSI.

[0072] As many apparently different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

We claim:
 1. A semiconductor integrated circuit device comprising: aclock signal generator; a plurality of flip-flops for receiving clocksignals from said clock signal generator through clock lines; and aplurality of stages of clock drivers furnished on said clock linesranging from said clock signal generator to said flip-flops; wherein anintermediate stage of said plurality of stages of clock drivers hasclock drivers each having a function for controlling clock signalsupplies; wherein a last stage of said plurality of stages of clockdrivers includes a first clock driver and second clock driver; andwherein said first clock driver has a function for controlling clocksignal supplies and said second clock driver does not have said functionfor controlling clock signal supplies.
 2. A semiconductor integratedcircuit device according to claim 1 , wherein said first clock driversare connected to flip-flops of data paths and said second clock driversare connected to flip-flops of random logic circuits or input/outputpads.
 3. A semiconductor integrated circuit device according to claim 2, wherein flip-flops of said data paths are not controlled individuallyand flip-flops of said random logic circuits and said input/output padsare controlled individually.
 4. A semiconductor integrated circuitdevice including a plurality of data paths comprising: a clock generatorsupplying clock signals through clock lines; a plurality of firstflip-flops arranged on one of the plurality of data paths; a pluralityof second flip-flops not arranged on any of the plurality of data paths;and a plurality of stages of clock drivers furnished on the clock linesranging from said clock signal generator to said plurality of firstflip-flops and said plurality of second flip-flops; wherein a firstclock driver included in a last stage of said plurality of stagessupplies clock signals to said plurality of first flip-flops; wherein asecond clock driver included in the last stage of said plurality ofstages supplies clock signals to said plurality of second flip-flops;wherein a said first clock driver has a function for controlling clocksignal supplies and said second clock driver has a function forcontrolling clock signal supplies; and wherein each of said plurality offirst flip-flops has no function for controlling clock signal suppliesand at least one of said plurality of second flip-flops has a functionfor controlling clock signal supplies.
 5. A semiconductor integratedcircuit device according to claim 4 , wherein said plurality of secondflip-flops are arranged in a random logic circuit or at a I/O padportions.
 6. A semiconductor integrated circuit device according toclaim 4 , wherein each of clock drivers of one of intermediate stage ofsaid plurality of stages has a function for controlling clock signalsupplies.
 7. A semiconductor integrated circuit device including aplurality of logic blocks comprising: a plurality of first flip-flopsarranged in a first area; a plurality of second flip-flops arranged in asecond area; a first plurality of stages of clock drivers furnished onfirst clock lines ranging from a first root clock driver to saidplurality of first flip-flops; and a second plurality of stages of clockdrivers furnished on second clock lines ranging from a second root clockdriver to said plurality of second flip-flops; wherein no logic blockshave both a flip-flop included in said first area and a flip-flopincluded in said second area.